An international terrorist who was an acquaintance of Yuuji's father, and took him after Yuuji killed his father. He trains Yuuji to be an assassin, and has him complete missions for him. He is the main antagonist of Grisaia no Rakuen.

It is revealed that he is one who ultimately killed Asako by shooting her in the head. She survived initially, but died years later aftering training Yuuji.

Yuuji and Heath eventually fight, and Heath holds the upper hand most of the fight, and stabs Yuuji in the chest with a sword, but Yuuji kills him by stabbing him in the neck with a pen.